1. Field of the Invention
The present invention relates to a polygon mirror scanner for light writing for use in digital copiers, page printers, and the like.
2. Discussion of the Background
FIG. 4 is a schematic view illustrating a cross section of a conventional polygon mirror scanner. A rotary polygon mirror 1 has a disc-shaped plane polygon (an equilateral hexagon in FIG. 4), a cylindrical rotor 3 below the rotary polygon mirror 1, a head 1a above the rotary polygon mirror 1 in the center thereof and six side faces 1b on the periphery of the rotary polygon mirror 1.
The six side faces 1b on the periphery of the rotary polygon mirror 1 are mirror-finished smooth light reflection faces (mirror faces). The center of the head 1a, i.e., a center of gravity of the equilateral hexagon, has a hole, where a rotating shaft 2 fitted to the rotary polygon mirror 1 is inserted. In addition, the rotating shaft 2 has a curved surface at both ends thereof.
A magnet 4 has a cylindrical shape having an outer diameter which is almost equal to an inner diameter of the rotor 3, and is fixed inside the rotor 3 so as to be concentric with the rotating shaft 2 to form a rotor 10 for the polygon mirror scanner.
A bearing device 20, supporting the rotating shaft 2 of the rotor 10, includes a radial bearing 21, supporting the rotating shaft 2, a thrust bearing 22, receiving a thrust load of the rotating shaft 2, and a stator yoke 23, supporting the radial bearing 21. The radial bearing 21 is formed of a slide bearing, such as a bearing including an oil, and fixed by being pressed into or bonded to an inner circumferential surface of the stator yoke 23.
The thrust bearing 22 is formed of a slide bearing, e.g., a resin plate such as polyimide having good slidability and abrasion resistance, and fixed by being pressed into or bonded to a concave part on the bottom of the inner circumferential surface of the stator yoke 23. The bearing device 20 is vertically fixed to a plane surface of a control base plate 32, and a coil 31 is fixed on a peripheral surface of the bearing device 20 to form a stator 30.
The coil 31 may be fixed on the control base plate 32. In addition, a peripheral cylindrical surface of the coil 31 faces a peripheral cylindrical surface of the inner circumferential and cylindrical surface of the magnet 4, while maintaining a predetermined clearance. Electricity from the control base plate 32 to the coil 31 drives the rotary polygon mirror 1 to rotate around the rotating shaft 2.
Conventionally, a rotary polygon mirror for use in a polygon mirror scanner for copiers, and like devices is constituted of a flat member having a mirror finished surface on its circumference. The mirror finished rotary polygon mirror is assembled with a rotor and a magnet to form a rotor for a scanner motor, i.e., a rotor for the polygon mirror scanner. The rotary polygon mirror is assembled with a rotating shaft, a rotor yoke, and a magnet to form a rotor for the polygon mirror scanner.
A stator works as a motor driving the rotary polygon mirror to rotate a scanning light beam, wherein a coil is arranged facing the magnet installed in the rotor with a predetermined space and a rotating shaft of the rotor is supported on a base plate on which a controller switching an energizing level of the coil is located.
Due to recent increasing environmental concerns, it is essential that electrical and mechanical products are reused and recycled. Therefore, individual components for digital copiers, page printers, and other similar devices need to be reused and recycled.
It has been said that a rotating shaft and a bearing for a polygon mirror scanner for light writing for use in the digital copiers, page printers, and the like can only be reused as a recycled metallic material or disposed of because, over time, they cannot avoid abrasion and damage due to their extended use.
However, a rotor including a rotary polygon mirror of a polygon mirror scanner for light writing, a rotating shaft, a rotor and a magnet in a body has less abrasion and damage of the rotating shaft due to its extended use. On the other hand, the bearing cannot avoid abrasion and damage due to its extended use.
Therefore, when the bearing comes to the end of its useful life, the polygon mirror scanner has to be exchanged as an assembly, although some of its components are still in a good and useful condition. In addition, a precise modification of the rotary polygon mirror of the rotor requires a significant amount of time and energy; therefore, the rotary polygon mirror has to be reused.
Japanese Laid-Open Patent Publication No. 2000-41359 discloses a method of removing only a rotating shaft from a motor frame and recycling other members thereof.
In the above-mentioned conventional polygon mirror scanner for light writing, the bearing is abraded by a contact of the rotating shaft when the rotation stars and stops because the rotating shaft, which is a center of rotation, is formed of a material harder than that of the bearing.
In addition, over an extended period of use, the rotational load deteriorates as a result of, as for example, a loss in lubrication. In these situations, the polygon mirror scanner takes longer to reach a stable rotational high-speed and experiences operational difficulties, including an irregular rotation and difficulty in maintaining a desired high-speed. These operational problems result in an increase of electric power consumption and a reduction in efficiency of the polygon scanner mirror.
Therefore, when the bearing comes to the end of its useful life, the polygon mirror scanner is exchanged as an assembly although some of its components have not come to the end of their useful lives, resulting in the unnecessary replacement of the good components.
In addition, it is not possible to replace the bearing without replacing the stator yoke into which the bearing is pressed, resulting in alteration and/or loss of the required high vertical precision or tight tolerances between the stator yoke to and the bottom surface of the motor circuit board due to current repair methods, thus, it becomes difficult to reach the needed high rotational speed and desired high efficiency for the polygon mirror scanner.
For at least the foregoing reasons, a need exists for a polygon mirror scanner having a bearing that can be easily replaced at the end of its useful life, while continuing to use other components in the mirror assembly that are still in good operating condition and maintaining the required high precision and tight tolerances for proper and efficient operation of the mirror assembly.